Gale Warning 107, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
431 PM AKST Sun Feb 2 2020

.ANALYSIS AND UPPER LEVELS...
Upper-level ridging currently over the eastern Gulf into Yukon
Territory is moving eastward ahead of a front over Kodiak Island
through southwest Alaska. A deep low currently centered 250 nm
southeast of Shemya has an occluded front moving northwestward
across the Bering. A trough axis associated with this low extends
southwestward into the north Pacific. A broad upper-level trough
extends northwestward from the aforementioned low into Russia.
The polar jet remains south of 50N through 155W and then extends
northeastward into the central Gulf of Alaska; the jet then
sharply dips southeastward into central California. The
subtropical jet remains south of 30N throughout the north Pacific.

At the surface, radar imagery shows snow bands moving
northeastward through the Kuskokwim Delta and Bristol Bay.
Observations show Gale force southeasterly winds from the north
shore of the Alaska Peninsula through Nunivak Island. ASCAT data
shows storm force winds on the western side of the low where steep
pressure gradients are present.

&&

.MODEL DISCUSSION...
Models are in good agreement with the overall synoptic pattern
across the area through mid-week. However, there are significant
mesoscale differences by Monday. The high resolution NAMNest was
favored in this forecast package with respect to the gap winds
across the Aleutians as this model has best handled the real-time
observations across the area. The NAMNest was also the preferred
model with respect to the barrier jet along the Gulf coast,
though hand edits were made to increase the wind speeds in this region.

&&

.AVIATION...
PANC...VFR conditions and light surface winds will continue
through the TAF period. A few flurries are possible this
afternoon as an upper level front pushes through Anchorage that
could drop ceilings briefly below 5000'. Due to a strong
southeasterly barrier jet and northerly surface winds, low level
wind shear is likely into Monday morning. Pireps have already
indicated some moderate turbulence between 1,000-2,000' this
afternoon.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)...

A front moving across Southcentral is currently bringing snow and
blowing snow to the eastern Kenai Peninsula. While the heaviest
snow and strongest winds are expected to remain east of the Seward
Highway, periods of reduced visibility are still likely.
Persistent low visibility remains forecasted for Portage Valley as
snow rates will be heaviest there. A Winter Weather Advisory
remains in effect through early Monday morning. Snow totals in
Whittier will likely exceed a foot. The Susitna Valley will also
see accumulating snow through Monday morning, although highest
totals will remain west of the Parks Highway. That said, wind
gusts up to 15 mph are possible between Talkeetna and Cantwell and
brief periods of reduced visibility are possible along that
stretch of road, particularly this evening.

As the front approaches the Gulf coast tonight, gusty
southeasterly winds will develop along Turnagain Arm, peaking near
60 mph around midnight. Snow will also subsequently develop in
the Cordova/Valdez areas, however, it will remain light. Easterly
storm force winds remain likely offshore south of Hinchinbrook
Entrance.

A low will track into the Gulf from the southwest Monday into
Tuesday. There remains uncertainty with regards to the exact
track, although it is likely to bring light accumulating snow to
much of Southcentral, to include the Anchorage Bowl Tue morning.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Tonight
through Wednesday):

A trio of fronts associated with a strong low over the Bering
will be affecting the area from tonight through the day on Monday.
The first front is affecting the area presently. Winter Weather
Advisories remain in effect over the Kuskokwim Delta and Bristol
Bay. Once the front passes, the precipitation rates should
diminish and allow temperatures to rise just above freezing for
most coastal locations. As the front dissipates over the area
tonight, scattered snow showers are expected.

The second front moves into Southwest Alaska during the day on
Monday. Since this second front won't be nearly as strong, winds
should not be as much of an issue. Widespread light snow amounting
to 1 to 3 inches for most areas are expected. Cloudy skies with
relatively warm temperatures in the 20s and 30s are expected
behind it.

The third front moves in Tuesday night into Wednesday, bringing
yet another round of light snow to most areas of Southwest Alaska.
With each front, coastal locations and the windier gap areas could
warm above freezing, bringing the possibility of rain or a
rain/snow mix to those areas. A strong, but slow-moving cold
front will approach Hooper Bay and the northern-most areas of the
Kuskokwim Delta late on Wednesday. There remains some model
disagreement on how far south it will dip in the days ahead.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3:
Tonight through Wednesday)...

A strong, but slowly weakening low approaching the central
Aleutians is the parent system of a series of fronts that extend
east and northeast from the low. The occluded front extends
northeast from the low center, and is moving into Southwest
Alaska. Widespread gales are ongoing in the waters around Saint
Matthew Island, extending southward to the western Aleutians. A
second front is forming behind it and is moving towards the
Pribilofs and the eastern Aleutians. Both fronts are moving
northeastward. Unsettled weather and plentiful cloud cover extend
over much of the Bering, and will persist over the next three
days. The low center is expected to track east of Atka Monday
evening, then move over the Pribilofs Tuesday afternoon. It will
then elongate as a secondary North Pacific low moves over the
central Aleutians as some of the energy moves into Southwest
Alaska. The low over the central Aleutians will become the main
low Wednesday afternoon and evening, but small spin-up lows are
possible all along a sharp front that will be nearly stationary
over the northern Bering. This front will eventually become a cold
front and begin moving southward late on Wednesday, though how far
it gets remains uncertain. What can be said for certain is that
the cold air will remain bottled up over the northern and western
Bering through Wednesday, so the Aleutians through the Pribilofs
will have an extended period of time of temperatures above
freezing in the 30s with some 40s as well.

&&

.MARINE (Days 3 through 5: Wednesday through Friday)...

...Bering Sea and Aleutian Coastal Waters...

Sustained gales are anticipated on Wednesday for the northern
Bering Sea, as the region will get sandwiched between an area of
high pressure over eastern Siberia and an area of low pressure,
with an attendant warm front, moving into the southern Bering.
Here, seas will peak near 20 feet. Lighter winds will prevail
elsewhere for Wednesday. All locations will remain below gales for
Thursday.

On Friday a stronger area of low pressure and warm front will
make its way into the southern Bering. With the Siberian high
remaining in place, sustained gales will spread from the western
portions of the sea towards the Pribilof Islands by Friday
evening. Given a longer fetch length than its predecessor, seas
will increase to near 20 feet from Dutch Harbor westward towards
Shemya south of the chain, with similar heights spreading from the
western Bering towards the Pribilof Islands.

...Gulf of Alaska...

Mainly quiet conditions are expected for the area, with winds
briefly reaching 20 to 30 knots for coastal locations near Kodiak
Island in the Wednesday evening through Thursday morning time
frame. Otherwise, look for seas to average in the 8 to 12 feet
range near the Gulf Coast, with slightly higher seas expected
offshore.

&&

.LONG TERM FORECAST (Days 3 through 7: Wednesday through
Sunday)...

An active weather pattern will be present for the duration of the
long term. Quick moving flow will cause a series of upper level
ridges and troughs to work their way across the Bering Sea and
across Southcentral AK. The long term starts with low pressure in
the Bering, creating stormy conditions there. Southwest flow
riding over the top of a ridge in the North Pacific can be
expected to create active weather (at least a chance of snow) and
warming conditions for Southcentral AK. From there, the long term
plays out with these systems working their way east.

Unfortunately, there is little model agreement on the timing and
placement of the individual weather features within this active
weather pattern. Therefore, all we can really say at this point
is to expect a series of storms to work their way across the
Bering and the Gulf of Alaska, with breaks in the weather in
between. One thing we can say is the pattern looks warm, so we can
expect the colder temperatures we have been seeing to slowly trend
warmer, especially for coastal areas.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisories 155 161 125.
MARINE...Heavy Freezing Spray Warnings 185.
		 Storm Warnings 119.
		 Gale Warnings 351 352 120 130 131 139 411 412 165 177
				       178 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...BL/ED
SOUTHCENTRAL ALASKA...AP
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JW
MARINE/LONG TERM...PD/BB